1. Field of the Invention
The present invention relates to a lighting device, in particular, a lighting device which is capable of varying a lighting angle and a photographing device using the lighting device.
2. Related Background Art
Regarding a lighting device used for a photographing device such as a camera, in order to converge a light beam outgoing from a light source in various directions to the interior of an angle of irradiated necessary view with a high luminous efficacy, there have been proposed various lighting devices up to now. In particular, in recent years, there has been proposed that an optical member using total reflection such as a prism or a light guide is disposed instead of a Fresnel lens disposed in front of the present light source to thereby improve a convergent efficiency and downsize the device.
On the other hand, in a lighting device of the irradiated area fixing type, a light is irradiated onto an unnecessary area in a telescopic state narrow in an irradiated area with a higher zooming magnification of the photographing device, and as the result, an energy loss is increased. In order to solve this phenomenon, there have been conventionally proposed various irradiating angle variable lighting devices that conduct lighting so as to be adaptive to the photographed area.
As a known technique of the lighting system to which the above two kinds of techniques are applied, there has been proposed in Japanese Patent Application Laid-Open No. 4-138439 by the present applicant, that the positional relation between the optical prism and the light source is relatively changed to change over between reflection and transmission to change the irradiated area with respect to a convergent optical system that conducts total reflection by an optical prism. Also, as disclosed in Japanese Patent Application Laid-Open No. 8-262538, there has been proposed a technique in which an optical prism is divided into a plurality of prisms, and the optical prisms disposed at upper and lower positions are rotated to change over the irradiated area.
In recent years, in the photographing device such as a camera, while the device per se is being progressively small-sized and lightened in weight, a photographing lens is intended to make the zooming magnification higher. In general, to make the photographing device small in size and high in magnification has a tendency to make the photographing lens gradually dark, and if photographing is made without using an auxiliary light source, there is a possibility that photographing unexpectedly fails due to vibrations by user""s hand.
In order to overcome the above circumstance, a lighting device (hereinafter referred to as xe2x80x9cstrobe devicexe2x80x9d) is normally integrated into the photographing device such as a camera as an auxiliary light source. However, the frequency of using the auxiliary lighting device is remarkably increased as compared with the conventional one in the above circumstances, and the amount of emission required every photographing is also intended to increase.
Under the above background, in the above conventional example disclosed in Japanese Patent Application Laid-Open No. 4-138439, an outgoing light from a flash discharge tube is divided into upper and lower total reflection control optical path and a face refraction control optical path by an optical prism to control those lights to a given convergent state, respectively, and the position of the light source is shifted from this state so that the total reflection optical path changes over between the total reflection and the transmission to conduct control by another optical path, and the refraction optical path changes the irradiated area so that the irradiating angle is widened.
However, in order to accurately vary the irradiating angle in the above proposed system, because a limit of the face configuration of changing over the total reflection and the transmission is large, there arise such serious problems in the optical design that the degree of freedom of designing the optical prism configuration is small, a light amount loss when the transmitted component of light incomes and outgoes becomes large, and a size of the effective light emitting portion of the light source largely contributes to light distribution.
On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 8-262538 (U.S. Pat. No. 5,813,743), there has been proposed that an optical prism is divided into a plurality of prisms, and optical prisms disposed on upper and lower portions are rotated to change over the irradiated area.
However, in the rotation of the optical prism, because only the irradiating direction of the totally reflected light component is basically wholly shifted, but light distribution characteristic per se is not changed, uniform light distribution is not always obtained at the respective zooming points. That is, the above proposal takes a system in which when those three upper, lower and center areas are overlapped with each other, the most convergent state is formed, and the optical prism is rotated from that state to gradually shift the upper and lower light distributions toward the outer side, to thereby widen the irradiated area. However, during a process of this change, discontinuous points occur on a portion where the respective upper, lower and center light distributions are overlapped with each other, whereby uniform distributions are not always obtained over the entire irradiated area, and a nonuniform point that produces the unevenness of illumination partially exists. Also, because the above structure requires those three upper, lower and center optical prism members, and two optical prisms must be moved in synchronism with each other, there arises such a problem that the structure of the mechanical parts is complicated, and the costs are raised.
As the other prior art, there are U.S. Pat. Nos. 5,539,622, and 6,022,117 proposed by the present inventors.
The present invention has been made under the above circumstances, and therefore an object of the present invention is to downsize the entire configuration of a lighting optical system and to vary an irradiating angle. Also, another object of the present invention is to unify the light distribution characteristic on the respective zoom points and to reduce the amount of movement caused by a variation of the irradiating angle. Still another object of the present invention is to reduce the number of structural parts to reduce the costs.
Further, still another object of the present invention is to provide an irradiating angle variable lighting device which is small-sized, thin and light in weight. Also, still another object of the present invention is to provide a lighting device such as a still camera or a video camera which utilizes an energy from a light source with a high efficiency, which obtains the uniform light distribution characteristic on the respective zoom points and which is simple and inexpensive in structure, and a photographing device using such a lighting device.
In order to achieve the above object, according to the present invention, there is provided an irradiation angle variable lighting device, comprising:
light source means (discharge tube); an optical prism disposed in front of the light source means for totally reflecting at least a part of an incident light beam from the light source means to irradiate the light beam onto an object to be photographed; and
first (panel) and second optical members (front window) disposed on a side of the object to be photographed of the optical prism;
wherein a relative displacement of the first and second optical members is changed to vary an irradiating angle.
In particular, the optical prism comprises: a light outgoing surface; a total reflecting surface; a first light incident surface that refracts a light from the light source means for directly guiding the light to the light outgoing surface; and a second light incident surface for guiding the incident light to the total reflection surface and guiding the light reflected by the total reflection surface to the light outgoing surface.
Also, the optical prism is structured so that the light beam refracted by the first light incident surface and the light beam reflected by the second light incident surface and the total reflection surface are in parallel with each other on a given section.
Also, the light beam refracted by the first light incident surface and the light beam reflected by the second light incident surface and the total reflection surface are substantially in parallel with an outgoing optical axis of the lighting device.
In particular, assuming that an inclination of the second light incident surface with respect to the outgoing optical axis is xcfx86, the following condition is satisfied.
0xc2x0xe2x89xa6xcfx860 less than 2xc2x0
Also, the first optical member includes a plurality of lens portions each having a convergent function on the given section, and the second optical member includes a plurality of lens portions each having a divergent function on the given section.
Pitches between the respective lens portions of the first optical member and the second optical member in a direction along which the respective lens portions are arranged are identical with each other, and the paraxial focal distances of the respective lens portions on the given section thereof are identical with each other, and assuming that the pitches are p and the paraxial focal distances are D, the following conditional expression is satisfied.
p/2xe2x89xa6Dxe2x89xa62p
Also, there is an embodiment in which the pitches between the respective lens portions and the paraxial focal distances of the respective lens portions on the given section thereof are different from each other.
Further, the light source comprises a discharge tube, and when a longitudinal direction of the discharge tube is an axial direction of the discharge tuber, the first and second optical members include a plurality of lens portions arranged in parallel with the axial direction.
In particular, each of the lens portions are made up of a cylindrical portion.
In this example, assuming that the pitches of the respective cylindrical lenses of the first optical member and the second optical member in a direction along which the respective cylindrical lenses are arranged are identical with each other, and the paraxial focal distances on sections of the first and second optical members taken along faces perpendicular to the axial direction are identical with each other, and assuming that the pitches are p and the paraxial focal distances are D, the following conditional expression is satisfied.
p/2xe2x89xa6Dxe2x89xa62p
Also, the respective lens portions on the sections perpendicular to the axial direction in the first optical member include a convergent function, and the respective lens portions on the sections perpendicular to the axial direction in the second optical member include a divergent function.
Further, the photographing device according to the present invention may includes the above irradiating angle variable lighting means. Note that the relative displacement referred to at the beginning, indicates, relative interval, that is, varying of the interval in the direction of outgoing optical axis, and shifting in the direction of outgoing optical axis in a vertical direction.
Other features of the present invention will become clear from the following description.